1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating a metal gate of the semiconductor device, and more particularly, to a complementary metal oxide semiconductor (CMOS) device having a low sheet resistance characteristic and a high diffusion barrier characteristic and a method of fabricating a metal gate of the CMOS device.
2. Description of the Related Art
A complementary metal oxide semiconductor (CMOS) device formed to be complementarily operated includes a p-channel metal oxide semiconductor (PMOS) transistor and an n-channel metal oxide semiconductor (NMOS) transistor. Such CMOS devices have increased efficiency and operation speed and also can have characteristics similar to a bipolar transistor. Thus, the CMOS devices are used as high speed and high performance devices.
In the prior art, a gate of a CMOS device is formed by forming a polysilicon doped to identical type to each channel on a gate insulating film (or a gate oxide film), for example, formed of silicon oxide SiO2. For example, a gate of the PMOS transistor is formed using polysilicon doped with a P-type dopant, and a gate of the NMOS transistor is formed using polysilicon doped with an N-type dopant. However, due to the high integration of the semiconductor devices, thicknesses of thin films in the semiconductor devices are gradually reduced. Thus, as the thickness of the conventional SiO2 thin film used as a gate insulating film is reduced, the leakage current is increased due to tunneling, and thus, power consumption of the CMOS device exceeds a standard value.
In order to address the above problems, studies have been conducted on developing a high dielectric (high-k) oxide film that can realize a gate insulating film electrically having a thickness identical to an equivalent oxide film thickness and physically having a thickness greater than a thickness that does not cause tunneling. As a result, SiO2 has been replaced with a high-k material such as HfO2 or Al2O3. However, when the high-k material is used as the gate insulating film, impurities included in the doped polysilicon formed on the gate insulating film are diffused into the gate insulating film.
Therefore, in order to address the diffusion problem, recently, studies have been conducted to use a metal as the gate instead of the doped polysilicon. The metal gate is also believed to decrease the high sheet resistance problem of conventional polysilicon. However, if a pure metal is used to obtain low sheet resistance, the diffusion problem still remains. Thus, attempts to use a metal compound such as TiN or TaN instead of a pure metal have been conducted. However, TiN and TaN are easily oxidized since TiN and TaN are highly oxidative. Also, problems of thermal stability and diffusion into the gate insulating film still remain.